1. Technical Field of the Invention
The invention relates generally to communication systems; and, more particularly, it relates to transmitter modules implemented within communication devices employed within such communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera, communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to an antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies them. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
While transmitters generally include a data modulation stage, one or more IF stages, and a power amplifier, the particular implementation of these elements is dependent upon the data modulation scheme of the standard being supported by the transceiver. For example, if the baseband modulation scheme is Gaussian Minimum Shift Keying (GMSK), the data modulation stage functions to convert digital words into quadrature modulation symbols, which have a constant amplitude and varying phases. The IF stage includes a phase locked loop (PLL) that generates an oscillation at a desired RF frequency, which is modulated based on the varying phases produced by the data modulation stage. The phase modulated RF signal is then amplified by the power amplifier in accordance with a transmit power level setting to produce a phase modulated RF signal.
As another example, if the data modulation scheme is 8-PSK (phase shift keying), the data modulation stage functions to convert digital words into symbols having varying amplitudes and varying phases. The IF stage includes a phase locked loop (PLL) that generates an oscillation at a desired RF frequency, which is modulated based on the varying phases produced by the data modulation stage. The phase modulated RF signal is then amplified by the power amplifier in accordance with the varying amplitudes to produce a phase and amplitude modulated RF signal.
As yet another example, if the data modulation scheme is x-QAM (16, 64, 128, 256 quadrature amplitude modulation), the data modulation stage functions to convert digital words into Cartesian coordinate symbols (e.g., having an in-phase signal component and a quadrature signal component). The IF stage includes mixers that mix the in-phase signal component with an in-phase local oscillation and mix the quadrature signal component with a quadrature local oscillation to produce two mixed signals. The mixed signals are summed together and filtered (optionally) to produce an RF signal that is subsequently amplified by a power amplifier.
As the desire for wireless communication devices to support multiple standards continues, recent trends include the desire to integrate more functions on to a single chip. However, such desires have gone unrealized when it comes to implementing baseband and RF on the same chip for multiple wireless communication standards. In addition, many components and/or modules within the components employed within such communication devices and wireless communication devices include many off-chip elements.
Within the transmitter portions of typical prior art devices, the gain adjustment of a signal that is ultimately transmitted (e.g., a radio frequency (RF) output signal) is typically performed exclusively within the analog domain. The control of any analog gain associated components is also typically performed exclusively within the analog domain within prior art communication devices. Oftentimes, this incurs the need for one or more analog transmit RF filter modules to perform the appropriate filtering within this prior art, analog architecture. A more complex and/or congested analog architecture typically and inherently results in a noisier analog cell within a communication device and/or integrated circuit. For example, in typical prior art architectures that are relatively more complex in nature, the use of one or more analog transmit RF filter modules, among other possible additional modules, may be needed to compensate for the relatively increased noise intrinsic to such prior art, complex and/or congested analog architectures.
In addition, because of the nature of such an analog architecture, such transmitters suffer from poor gain stability over temperature, process, and/or power supply variations. This prior art approach makes it very difficult to implement any transmitter design that is not susceptible to these deleterious effects. Also, the very nature of such prior art approaches has a high sensitivity to noise. Also, in some prior art embodiments, there may be no power savings within such a prior art communication device when it operates with relatively lower output power levels. Moreover, given the inherently coupled nature of components within such prior art analog architectures, there can be great difficulty in the independent adjustment of components therein. Setting any gain value with a relatively high degree of accuracy can be virtually impossible within such prior art architectures. As a result, the transmit signal accuracy of such prior art architectures suffers significantly from in-phase/quadrature (I, Q) gain and phase errors.
There exists a need in the art for a means by which better transmitter architectures may be implemented within communication devices (including wireless communication devices).